The present invention relates to a sole structure of an athletic shoe, and more particularly, a sole structure that has a wavy plate inserted between an upper midsole and a lower midsole.
A sole for an athletic shoe used in various sports includes a midsole and an outsole that is fitted on the bottom surface of the midsole and directly contacts the ground. The midsole is generally formed of a soft elastic material to ensure adequate cushioning properties as a shoe.
Incidentally, as a sports shoe, not only cushioning properties but also running stability is required. That is, there exists a need to prevent excessive lateral or transverse deformation of a sole, such as pronation or supination occurring at the time of striking onto the ground.
In order to prevent such a lateral deformation, as shown in Japanese patent application laying-open publication No. 11-203, Mizuno Corporation proposed a midsole structure having a wavy plate with a corrugation inserted thereinto. In this case, by the action of the wavy plate, a resistance force occurs to restrain a heel portion of a midsole from deforming in the transverse direction at the time of impacting onto the ground, thereby preventing the heel portion of a shoe from laterally deforming.
Such a wavy plate prevents lateral deformation of a shoe, but it decreases cushioning properties of the whole midsole. In the midsole structure shown in the above-mentioned publication, amplitude of a corrugation of a wavy plate is suitably varied between a front end and a rear end or between a medial side and a lateral side of the shoe heel portion to achieve cushioning properties. Although such a method of securing cushioning properties and preventing lateral deformation was adequate for runners whose pronation or supination is not so great, but it was inadequate for runners whose pronation or supination is greater. In athletic sports, such as tracks, field events, tennis, volleyball, basketball, or the like, an impact load three to five times an athlete""s weight is applied on landing and especially on jumping, very high impact load about ten times an athlete""s weight is applied. In these sports, adequate cushioning properties were not necessarily achieved by the above-mentioned midsole structure.
The present invention has been made in view of these conventional circumstances, and its object is to provide a sole structure of an athletic shoe that can not only effectively absorb an impact load applied to a heel portion of the shoe directly after contacting the ground but also securely prevent a pronation or supination of a shoe wearer""s foot.
A sole structure of an athletic shoe according to a first invention includes an upper midsole that is formed of a soft elastic material and that extends from a heel portion of the shoe to a forefoot portion through a midfoot portion, a lower midsole that is formed of a soft elastic material and that is disposed at least at the heel portion of the shoe under the upper midsole, a wavy plate or a corrugated sheet having a wavy corrugation that progresses from a rear end side of the heel portion toward the midfoot portion and that is provided at least at the heel portion between the upper and lower midsoles, an outsole that is fitted on the bottom surface of the lower midsole, and a shock absorbing member that is fitted at a xe2x80x9cheel strike regionxe2x80x9d of the heel portion of the shoe between the wavy plate and the outsole.
Here, the term, xe2x80x9cheel strike regionxe2x80x9d used herein means a region of the heel portion of a shoe that contacts the ground at a first stage of landing when a shoe wearer lands on the ground from the heel portion of the shoe.
As a xe2x80x9cshock absorbing memberxe2x80x9d, a high molecular compound having viscoelasticity is preferable. Specifically, polystyrene, polyurethane, or polyisoprene elastomer may be utilized. Also, a blend type of these mixed elastomers, or both solid and foamed types are included. The wavy plate is preferably formed of thermoplastic resin or thermosetting resin.
In this first invention, an impact load applied to the heel strike region of the shoe heel portion directly after contacting the ground is effectively absorbed by the shock absorbing member fitted at the heel strike region. And after landing onto the ground, pronation or supination of a shoe wearer""s foot is securely prevented by the action of the wavy plate.
Also, in this case, because the shock absorbing member is provided between the wavy plate and the outsole, that is, on the side of the lower midsole, stability of the shoe heel portion on landing is secured to some extent by the upper midsole, and the impact load applied to the outsole is absorbed by the shock absorbing member. In contrast, when the shock absorbing member is provided on the upper midsole side, that is, between the upper and the wavy plate, lateral deformation of the shoe heel portion is easy to occur on landing and stability of the shoe heel portion is hardly maintained.
In a sole structure of an athletic shoe according to a second invention, the shock-absorbing member is formed of a viscoelastic material having 70% or more energy loss, or preferably, 85% or more energy loss.
Here, the term, xe2x80x9cviscoelasticityxe2x80x9d used herein means a phenomenon in which deformation caused by an external force appears as an overlap of elastic deformation and viscous flow, and such properties are especially remarkably seen in high molecular compound.
When an impact force is applied to the viscoelastic material, a portion of supplied energy by the impact force is converted into heat energy and the like, and by the amount of the converted energy, the impact force is absorbed and a shock is relieved. On the other hand, the other portion of supplied energy, which is not liveried converted into heat energy and the like, restores the deformed viscoelastic material to its original condition before deformation as a restoring energy by elastic rebound. In this case, the amount of supplied energy minus the restoring energy is an energy loss.
Generally, 70% or 85% or more energy loss is considerably high value. When a shock absorbing member formed of only a viscoelastic material having such a high energy loss is provided in the midsole, a shoe wearer receives a feeling of floating from the ground during activities, especially running, and as a result, he or she cannot exert a necessary kick power to the ground at the start of running and cannot control activities.
In contrast, according to the present invention, since such a shock absorbing member is used with the wavy plate, compressive and lateral deformations of the upper and lower midsoles after landing are restrained by the action of the wavy plate. Thus, a shoe wearer can exert a sufficient kick force to the ground and control activities.
In other words, as in the present invention, that the wavy plate is provided in the midsole enables to use the shock absorbing material formed of a viscoelastic material having 70% or more, or 85% or more high energy loss.
According to the present invention, even in sports where very high impact force is applied on jumping, a shock applied to the shoe heel portion is absorbed and relieved by the shock absorbing member having 70% or more, or 85% or more high energy loss, and lateral deformation of the shoe heel portion is prevented and activities are controlled by the action of the wavy plate.
In a sole structure of an athletic shoe according to a third invention, the shock absorbing member has hardness of 55 degrees or less, preferably, 45 degrees or less at Asker C scale. In this case, an impact force applied to the shock absorbing member is absorbed by converting a portion of supplied energy by the impact force into heat energy and the like. In addition, the reason why the hardness of 55 degrees or less at Asker C scale is employed is that less shock absorbing properties or less cushioning properties are acquired if the hardness is greater than 55 degrees at Asker C scale.
In a sole structure of an athletic shoe according to a fourth invention, the shock absorbing member extends along the outer circumference of the shoe heel portion and has a width of 10(mm) or more.
Here, the reason why the width of the shock absorbing member is limited to 10(mm) or more is that at least the width of 10(mm) is required to absorb a shock directly after contacting the ground. And the reason why the width over 10(mm) is allowed is that even when the shock absorbing member has the width over 10(mm) the whole midsole can be prevented from being excessively compressed by the action of the wavy plate.
In a sole structure of an athletic shoe according to a fifth invention, there exist inequalities, 0.1Lxe2x89xa6LLxe2x89xa60.5L and LMxe2x89xa60.1L.
Here, L: entire length of a horizontal projection plane of an outsole.
LL: length of a lateral side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
LM: length of a medial side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
In this case, since the lateral side region of the shock absorbing member is longer than the medial side region thereof, a shoe sole structure, which is suitable for sports such as tracks where landing frequently occurs on the lateral side, can be achieved.
Here, the reason why the elongated length LL of the shock absorbing member is limited to 0.1L or more is that at least the length of 0.1L is required to absorb a shock directly after landing on the lateral side. The reason why the elongated length LL is limited to 0.5L or less is as follows: It is sufficient that the shock absorbing member extends to the midfoot portion at the longest, and if the shock absorbing member has the length over 0.5L, it reaches the forefoot portion. Further, the reason why the elongated length LM is limited to 0.1L or less is that if the length is over 0.1L it promotes pronation.
In a sole structure of an athletic shoe according to a sixth invention, amplitude of a wavy configuration of the wavy plate at the heel portion is smaller on the lateral side and greater on the medial side. That is, moment of inertia of area of the wavy plate is greater on the medial side, and thus, compressive hardness, which represents hardness to compressive deformation of the whole midsole, is higher on the medial side.
This sixth invention exercises a superior effect when it is combined with the fifth invention. That is, in sports such as tracks, when a runner lands on the ground from the lateral side of the heel portion during running, the shock absorbing member on the lateral side absorbs a shock to the outsole directly after contacting the ground. And the medial side of the midsole having greater compressive hardness sustains leaning of foot toward the medial side of the heel portion after landing. In such a way, by interaction between the shock absorbing member and the wavy plate, a shock applied to the shoe heel portion directly after contacting the ground is effectively absorbed and pronation of a shoe wearer""s foot is securely prevented.
In a sole structure of an athletic shoe according to a seventh invention, there exist inequalities, LLxe2x89xa60.1L and 0.1Lxe2x89xa6LMxe2x89xa60.5L.
Here, L: entire length of a horizontal projection plane of an outsole.
LL: length of a lateral side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
LM: length of a medial side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
In this case, since the medial side region of the shock absorbing member is longer than the lateral side region thereof, a shoe sole structure, which is suitable for sports such as tennis or basketball where landing from the medial side and transverse movements frequently occur, can be achieved.
Here, the reason why the elongated length LM of the shock absorbing member is limited to 0.1L or more is that at least the length of 0.1L is required to absorb a shock directly after landing on the medial side. The reason why the elongated length LM is limited to 0.5L or less is as follows: It is sufficient that the shock absorbing member extends to the midfoot portion at the longest, and if the shock absorbing member has the length over 0.5L, it reaches the forefoot portion. Further, the reason why the elongated length LL is limited to 0.1L or less is that if the length is over 0.1L it promotes supination.
In a sole structure of an athletic shoe according to an eighth invention, amplitude of a wavy configuration of the wavy plate at the heel portion is smaller on the medial side and greater on the lateral side. That is, moment of inertia of area of the wavy plate is greater on the lateral side, and thus, compressive hardness, which represents hardness to compressive deformation of the whole midsole, is higher on the lateral side. This eighth invention exercises a superior effect when it is combined with the seventh invention. That is, in sports such as tennis, basketball, or the like, when a player lands on the ground from the medial side of the heel portion during a game, the shock absorbing member on the medial side absorbs a shock to the outsole directly after contacting the ground. And the lateral side of the midsole having greater compressive hardness sustains leaning of foot toward the lateral side of the heel portion after landing. In such a way, by interaction between the shock absorbing member and the wavy plate, a shock applied to the shoe heel portion directly after contacting the ground is effectively absorbed and supination of a shoe wearer""s foot is securely prevented.
In a sole structure of an athletic shoe according to a ninth invention, there exist inequalities, 0.1Lxe2x89xa6LLxe2x89xa60.15L and 0.1Lxe2x89xa6LMxe2x89xa60.15L.
Here, L: entire length of a horizontal projection plane of an outsole.
LL: length of a lateral side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
LM: length of a medial side region of a shock absorbing member measured from the rearmost end of the heel portion along the shoe elongated direction.
In this case, since the medial side region of the shock absorbing member has almost the same length as the lateral side region thereof, a shoe sole structure, which is suitable for sports such as walking where landing occurs on the central portion of the rear end side of the shoe heel portion, is achieved.
Here, the reason why each of the elongated lengths LL and LM of the shock absorbing member is limited to 0.1L or more is that at least the length of 0.1L is required to absorb a shock directly after landing on the rear central portion. The reason why each of the elongated lengths LL and LM is limited to 0.15L or less is as follows: It is sufficient that the shock absorbing member has the length of 0.15L at the longest to absorb a shock applied to the rear central portion, and if the shock absorbing member has the length over 0.15L, it may promote pronation and supination.
In a sole structure of an athletic shoe according to a tenth invention, amplitude of a wavy configuration of the wave plate at the heel medial portion is nearly equal to that of a wavy configuration of the wavy plate at the heel lateral portion. This tenth invention is suitable for a shoe such as a walking shoe where landing on the ground frequently occurs on the general central portion on the rear end side of the shoe heel portion.